A known example of X-ray mammography systems is disclosed in PTL 1, which includes a reflection type X-ray tube as an X-ray generating unit.
FIG. 4(a) illustrates the basic configuration of an X-ray mammography system 101 that includes a reflection type X-ray tube as an X-ray generating unit.
In FIG. 4(a), the X-ray generating unit 101 includes a target 102 and an electron emitting source 103. The target 102 is a reflection type target in which a target layer 102a that generates X-rays when irradiated with an electron beam is provided on a supporting substrate 102b that reflects X-rays. The radiation area of X-rays 118 generated when the target layer 102a is irradiated with an electron beam emitted by the electron emitting source 103 is defined by a collimator (not shown), and thus, a predetermined X-ray irradiated area is formed on a detecting portion 117 of an X-ray detecting unit 106 through a breast 105 of a testee 104.
The X-ray generating unit 101 is generally disposed such that the electron emitting source 103 is close to the testee 104, as shown in FIG. 4(a). Such placement causes the focal spot center 107 of the X-rays 118 to be viewed from a nipple 105a side at a larger angle than the chest side. This makes an apparent focal spot diameter of the X-rays 118 at the nipple 105a side smaller than that at the chest side, thus enhancing the resolution. This allows early detection of a calcified region, which tends to occur in the nipple 105a. Furthermore, this can increase radiation dose on the chest, where the distance of transmission of the X-rays 118 is large, thereby preventing a decrease in radiation dose on the chest.